1. Field of the Invention
The present invention relates to refractory metallic alloys exhibiting a high catalytic activity which are particularly useful for reducing exhaust gas pollution from automobiles.
2. Description of the Prior Art
In this area known methods, particularly for facilitating post-combustion of carbon monoxide and hydrocarbons, include the positive action of noble metals of group VIII of the periodic table of elements as well as that of the mixed oxides of copper, nickel, cobalt, manganese, etc., deposited on refractory supports such as porous alumina.
The preceding products generally have satisfactory activity when they are new but have, at the same time, the following disadvantages:
Mechanical fragility, as is well recognized.
The catalyst, if it is in pellet form, is significantly degraded in operation; if it is constructed as a monolith it is necessary to use relatively complex mounting means to avoid breakage by mechanical or thermal shock.
Reduction of activity, frequently irreversible, after over-heating or contamination. Accidental over-heating exceeding 1000.degree. C. is common, due both to the large amount of energy released by the combustion of unburnt hydrocarbons and the poor thermal conductivity of the refractory supports which hinders the rapid dissipation of heat;
Relatively difficult recovery of the platinum metals due to their great dilution in a mass of very refractory material.